The White House on Monday defended President Obama’s decision to enter into the Paris climate accord without Senate ratification but stopped short of confirming a Chinese report that he will do so this week during his trip to China.

Still, it would surprise no one if Mr. Obama and Chinese President Xi Jinping were to announce the ratification of the sweeping climate change agreement before the Sunday opening of the Group of 20 summit in Hangzhou, Zhejiang.

White House senior adviser Brian Deese said the president has the legal authority to ratify the accord without the two-thirds Senate vote required for treaties. He said the pact negotiated by 195 countries in December is merely an “executive agreement.”

“The president will use his authority that has been used in dozens of executive agreements in the past to join and formally deposit our instrument of acceptance, and therefore put our country as a party to the Paris Agreement,” Mr. Deese said at a White House press conference.

He noted that both presidents announced in March that they “would seek to formally join the Paris Agreement in 2016.”